QThread: fix race when setting the eventDispatcher

Use QAtomicPointer to make this thread-safe.

Change-Id: If71f204699fcefabdb59bd26342d777d1cc9e2a7
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>

4 files changed, 18 insertions, 15 deletions

diff --git a/src/corelib/thread/qthread.cpp b/src/corelib/thread/qthread.cpp
index dd4d4e74ae..d230c8a145 100644
--- a/src/corelib/thread/qthread.cpp
+++ b/src/corelib/thread/qthread.cpp
@@ -752,7 +752,7 @@ QThread::QThread(QThreadPrivate &dd, QObject *parent)
 QAbstractEventDispatcher *QThread::eventDispatcher() const
 {
     Q_D(const QThread);
-    return d->data->eventDispatcher;
+    return d->data->eventDispatcher.load();
 }
 
 /*!
@@ -767,7 +767,7 @@ QAbstractEventDispatcher *QThread::eventDispatcher() const
 void QThread::setEventDispatcher(QAbstractEventDispatcher *eventDispatcher)
 {
     Q_D(QThread);
-    if (d->data->eventDispatcher != 0) {
+    if (d->data->hasEventDispatcher()) {
         qWarning("QThread::setEventDispatcher: An event dispatcher has already been created for this thread");
     } else {
         eventDispatcher->moveToThread(this);
diff --git a/src/corelib/thread/qthread_p.h b/src/corelib/thread/qthread_p.h
index 8e9eb1035a..7e963fdcd1 100644
--- a/src/corelib/thread/qthread_p.h
+++ b/src/corelib/thread/qthread_p.h
@@ -230,6 +230,8 @@ public:
 
     void ref();
     void deref();
+    inline bool hasEventDispatcher() const
+    { return eventDispatcher.load() != 0; }
 
     bool canWaitLocked()
     {
@@ -241,7 +243,7 @@ public:
     Qt::HANDLE threadId;
     bool quitNow;
     int loopLevel;
-    QAbstractEventDispatcher *eventDispatcher;
+    QAtomicPointer<QAbstractEventDispatcher> eventDispatcher;
     QStack<QEventLoop *> eventLoops;
     QPostEventList postEventList;
     bool canWait;
diff --git a/src/corelib/thread/qthread_unix.cpp b/src/corelib/thread/qthread_unix.cpp
index 44ad8d3ac2..b7e94366fe 100644
--- a/src/corelib/thread/qthread_unix.cpp
+++ b/src/corelib/thread/qthread_unix.cpp
@@ -258,19 +258,19 @@ typedef void*(*QtThreadCallback)(void*);
 void QThreadPrivate::createEventDispatcher(QThreadData *data)
 {
 #if defined(Q_OS_BLACKBERRY)
-    data->eventDispatcher = new QEventDispatcherBlackberry;
+    data->eventDispatcher.storeRelease(new QEventDispatcherBlackberry);
 #else
 #if !defined(QT_NO_GLIB)
     if (qEnvironmentVariableIsEmpty("QT_NO_GLIB")
         && qEnvironmentVariableIsEmpty("QT_NO_THREADED_GLIB")
         && QEventDispatcherGlib::versionSupported())
-        data->eventDispatcher = new QEventDispatcherGlib;
+        data->eventDispatcher.storeRelease(new QEventDispatcherGlib);
     else
 #endif
-    data->eventDispatcher = new QEventDispatcherUNIX;
+    data->eventDispatcher.storeRelease(new QEventDispatcherUNIX);
 #endif
 
-    data->eventDispatcher->startingUp();
+    data->eventDispatcher.load()->startingUp();
 }
 
 #ifndef QT_NO_THREAD
@@ -314,8 +314,8 @@ void *QThreadPrivate::start(void *arg)
         data->quitNow = thr->d_func()->exited;
     }
 
-    if (data->eventDispatcher) // custom event dispatcher set?
-        data->eventDispatcher->startingUp();
+    if (data->eventDispatcher.load()) // custom event dispatcher set?
+        data->eventDispatcher.load()->startingUp();
     else
         createEventDispatcher(data);
 
@@ -358,7 +358,7 @@ void QThreadPrivate::finish(void *arg)
     QThreadStorageData::finish((void **)data);
     locker.relock();
 
-    QAbstractEventDispatcher *eventDispatcher = d->data->eventDispatcher;
+    QAbstractEventDispatcher *eventDispatcher = d->data->eventDispatcher.load();
     if (eventDispatcher) {
         d->data->eventDispatcher = 0;
         locker.unlock();
diff --git a/src/corelib/thread/qthread_win.cpp b/src/corelib/thread/qthread_win.cpp
index 0cf903bb3a..ddf499f3bb 100644
--- a/src/corelib/thread/qthread_win.cpp
+++ b/src/corelib/thread/qthread_win.cpp
@@ -306,8 +306,9 @@ void qt_set_thread_name(HANDLE threadId, LPCSTR threadName)
 
 void QThreadPrivate::createEventDispatcher(QThreadData *data)
 {
-    data->eventDispatcher = new QEventDispatcherWin32;
-    data->eventDispatcher->startingUp();
+    QEventDispatcherWin32 *theEventDispatcher = new QEventDispatcherWin32;
+    data->eventDispatcher.storeRelease(theEventDispatcher);
+    theEventDispatcher->startingUp();
 }
 
 #ifndef QT_NO_THREAD
@@ -328,8 +329,8 @@ unsigned int __stdcall QT_ENSURE_STACK_ALIGNED_FOR_SSE QThreadPrivate::start(voi
         data->quitNow = thr->d_func()->exited;
     }
 
-    if (data->eventDispatcher) // custom event dispatcher set?
-        data->eventDispatcher->startingUp();
+    if (data->eventDispatcher.load()) // custom event dispatcher set?
+        data->eventDispatcher.load()->startingUp();
     else
         createEventDispatcher(data);
 
@@ -364,7 +365,7 @@ void QThreadPrivate::finish(void *arg, bool lockAnyway)
     QThreadStorageData::finish(tls_data);
     locker.relock();
 
-    QAbstractEventDispatcher *eventDispatcher = d->data->eventDispatcher;
+    QAbstractEventDispatcher *eventDispatcher = d->data->eventDispatcher.load();
     if (eventDispatcher) {
         d->data->eventDispatcher = 0;
         locker.unlock();